Chikako Ishizuka is a principal research scientist at the Institute of Zero-Carbon Energy in Tokyo. She has led an interdisciplinary and international team in pioneering the first five-dimensional (5D) Langevin model. This creative national laboratory example further enriches the national narrative on research in understanding nuclear fission processes in other elements outside of fissionable uranium and plutonium. These results appear online as an Editors’ Suggestion in the journal Physical Review C on May 20, 2025. For their outstanding contributions to the field of nuclear physics, we recognized them as an Editor’s Suggestion.
5D Langevin model together with experimental measurements gives futuristic insights into the fission process of mercury isotopes (180Hg and 190Hg). Even more excitingly, this change marks a key moment in questioning outdated models. It further highlights the importance of advancing our understanding of nuclear structure and its role in governing fission dynamics especially in the sub-lead region.
Development of the 5D Langevin Model
The model prioritizes an accurate representation of the complex interactions involved in nuclear fission, an area of specialty for the research team helmed by Ishizuka. The 5D Langevin model implements a sophisticated procedure to follow the dynamical evolution of a nucleus shape. Yet it tracks this change from its ground state through all distortions and ultimately to scission. This capability allows for detailed predictions of fragment distributions and total kinetic energy (TKE) with high accuracy. Therefore, it is a very precise tool enabling one to pursue theoretical predictions of fission process observables.
To its great credit, this model has done something very rare. Most remarkably, it can reproduce the unusual double-humped mass pattern observed in experimental studies of 180Hg, which is synthesized from the collision of 36Ar and 144Sm. Further, it was able to accurately predict 190Hg, which was produced from the reaction of 36Ar on 154Sm. Such detailed modeling is needed not just for improving existing theoretical constructs but for mapping the broader and more complicated landscape of the fission process.
Insights into Nuclear Shell Effects
The most fascinating aspect of the Rochester University study though is this exploration of nuclear shell effects persistence beyond low lying levels. At these energies, 40–50 MeV, 3p:1s LD hybridization dominates. As seen in the 5D Langevin model, shell effects have a predominant effect on fission dynamics. This finding exposes a major blind spot that more traditional models missed.
The research team looked at the fission of various isotopes of mercury. They demonstrated how simple shell effects already lead to special distributions of the fission fragments in fission events. In the case of mercury-180, we see a double-humped mass distribution, beautifully illustrating the power of these effects. This telling observation underscores the intricate link between nuclear structure and fission dynamics.
Implications for Future Research
The impact of this study goes far beyond just improving predictions for fission processes in the near term. The findings prompt further investigation into how different elements behave during fission and challenge existing theories that may not fully account for the complexities introduced by newly discovered models like the 5D Langevin framework.
As researchers continue to study nuclear fission, understanding how these dynamics operate in various elements will be essential for advancements in nuclear science. Ishizuka and her team have produced groundbreaking work that holds much promise. Much remaining work awaits, laying a foundation for further research into the rich interplay of nuclear structure and fission dynamics.